The Liquid Crystal Display (LCD) with advantages of thin body, power saving and no radiation has been widely used in many applications, such as LCD TV, mobile phone, personal digital assistant (PDA), digital camera, notebook, laptop, etc., and dominates the flat panel display field.
The active matrix liquid crystal display (AMLCD) is the most popular display device currently. The AMLCD comprises a plurality of pixels, and each pixel connects a thin film transistor (TFT). The gate of the TFT is connected to the scan line extending along the horizontal direction. The source of the TFT is connected to the data line extending along the vertical direction. The drain of the TFT is connected to the corresponding pixel electrode. A sufficient positive voltage is applied to a scan line to switch on all the TFTs connected to the scan line, thereby to write the data signal of the data line into the pixel electrodes and to control the transmittances of different liquid crystals for achieving the effect of controlling colors and brightness.
The gate driver on array (GOA) technology utilizes the current process of fabricating array on the thin film transistor liquid crystal display panel to manufacture the driving circuit of gate lines on the TFT array substrate, for realizing the driving method of scanning the gate lines row by row. The GOA technology can reduce the bonding procedures for connecting the external integrated circuit (IC) and has potential to raise the productivity and reduce the cost. Meanwhile, it can make the liquid crystal display panel more suitable to the narrow frame or non-frame design of display products.
The metal oxide semiconductors, such as indium gallium zinc oxide (IGZO), have higher carrier mobility and good stability for devices. Therefore, using the metal oxide semiconductor thin film transistors for fabricating the GOA circuits can reduce the complexity, decrease the scales and numbers of the thin film transistors and the number of power supply for stabilizing the performances of the thin film transistors, thereby to simplify the structures of GOA circuits, achieve the display panel with narrow frame and reduce power consumption at the same time.
However, during the work process of GOA circuits, the threshold voltages of thin film transistors become the negative values frequently, thereby to lead to the malfunction of the GOA circuits. Especially, for the GOA circuits fabricated by applying the metal oxide semiconductor thin film transistors, the above issue is more serious.